1. Field of the Invention
The present invention relates to a structure for connecting an optical fiber to an interface box having a light receiving/emitting element.
2. Description of Related Art
Recently, an optical fiber is used for various purposes, e.g., as a transmitting line in a communication system or as a load sensor in a collision detecting system in an automobile. JP-A-07-190732 discloses a device for detecting an automobile collision using an optical fiber as a sensor. In this detecting device, an optical fiber is disposed along a front bumper, and one end of the optical fiber is optically connected to a light-emitting element and the other end is connected to a light-receiving unit. When the vehicle collides with another vehicle or an obstacle, the optical fiber may be broken or damaged, thereby reducing an amount of light being transmitted through the optical fiber. The collision is detected based on the amount of light received by the light-receiving unit.
An example of a device in which the optical fiber is used as a sensor for detecting a strain in a resilient rubber member is disclosed in JP-A-2002-236005. An elongate sensor having an optical fiber therein is embedded in the rubber member. An amount of load applied to the resilient rubber member is detected based on the strain detected by the sensor having the optical fiber. Since a light-transmitting phase in the optical fiber changes according to a strain, an amount of strain can be detected by detecting the changes in the light phase, using a light interference detector such as an optical fiber ring detector.
An optical fiber is composed of a core member and a clad member disposed around the core member. When the optical fiber is optically connected to another piece of the optical fiber or to a light-receiving and/or emitting element, it is important to avoid mismatching of light-emitting/receiving angle relative to the fiber axis (an angle θ between a light-emitting/receiving direction and the center axis of the optical fiber) at a point of optical connection. This is because a loss in light transmission occurs if there is mismatching.
An example of a structure for connecting an optical fiber to a light-receiving/emitting element is disclosed in JP-A-2001-013366. In this structure, a ferule in which an optical fiber is disposed is telescopically inserted into a receptacle having a light-receiving/emitting element therein. By telescopically inserting the ferule into the receptacle, mismatching of the light angles at the connecting point is minimized, thereby attaining an optical connection at low connection loss. The ferule further includes a door for protecting an exposed end of the optical fiber. The door is spring-biased and is opened only when the ferule is inserted into the receptacle and positioned to face the light-receiving/emitting element. The door is closed at other times thereby protecting the exposed end of the optical fiber.
The connecting structure disclosed in JP-A-2001-013366, however, is mostly intended for use in connection on a printed circuit board. In the case where an optical fiber connecting structure is used in an automobile, the connecting structure is always subjected to high vibration and possible water immersion. Therefore, it is necessary to provide the optical fiber connecting structure with strength against the vibration and water immersion when the connecting structure is used in an automobile.